It is five years since US president Barack Obama ended the controversial renditions, interrogations and detention program led by the Central Intelligence Agency under his predecessor George W Bush but he will have to deal with the fallout from a reignited scandal about the harsh techniques used against prisoners.

The US Senate Intelligence Committee, which is responsible for the oversight of the CIA, voted on Thursday to declassify the executive summary and conclusions of the long-anticipated 6,300 -page report into the program. This paves the way for the disclosure of details of treatments meted out to prisoners in actions that Amnesty International has said amount to torture.

Fresh details of how al-Qaeda suspects were treated, leaked to the Washington Post , revealed that CIA operatives dunked prisoners in tanks of ice water at one of its network of secret prisons or "black sites” in a method similar to waterboarding, a simulation of drowning, that was not signed off by the department of justice as an approved interrogation technique.

Concealed details

The Senate committee has reportedly concluded in the report that the CIA misled US Congress and the American people about the effectiveness of the interrogations by concealing details of the severity of the techniques used and by overstating that the methods used by the agency had yielded crucial pieces of intelligence, including a clue that led to the killing of al-Qaeda leader Osama bin Laden in 2011.

"The purpose of this review was to uncover the facts behind this secret program and the results were shocking,” said Senator Dianne Feinstein, a Democrat from California and chair of the Senate committee. "The report exposes brutality that stands in stark contrast to our values as a nation. It chronicles a stain on our history that must never again be allowed to happen.”

Before the findings can be made public, however, Obama must sign off on their publication and the White House also has to canvass the views of the CIA itself, a process Obama’s officials will not say how long will take. With the sensitivities around the content of the report, and the likely damage it would cause the current US administration, the full details about some of the darkest and ugliest practices in US intelligence history will be kept in secrecy for some time to come.